EVP are sounds recorded either digitally or on magnetic tape that are usually called "ghost voices."
Following is an excerpt from What is EVP and is it real? by BMGH member Richard A. Barker.
To read the complete article, please visit PhoenixParanormal.org, the investigative and research division of Big Muddy Ghost Hunters. BMGH members must complete training and become a Certified Paranormal Investigator to take part in investigations.
What is EVP and is it real?
by Richard A. Barker
"EVP can be classifiedinto three catagories: Catagory One is a recorded phenomenon that anyone can recognize as spoken words with a specific, coherent meaning. Category Two is a recorded phenomenon that most people can decipher with some coaching. Catagory Three is a recorded noise that is unexplained, but that does not convey anything that most listeners would recognize.
"If, in the process of an investigation, a recorded voice says, "Why did you drop the ball during the softball game last Sunday?" or comments on your choice of wearing purple shoes with orange pants, or knows some obscure detail about your grandmother that no one else knows, and these observation are true, it will be hard to explain away your results as stray sound or radio phenomena. You may have a genuine ghost.
"The pervasive theory for how ghosts record their voices is that they "shape" noise in the environment into electronic sounds. EVP seem to occur more frequently when there is electromagnetic disturbance in the atmosphere, such as thunderstorms or sun spots. Some EVP researchers use a television or radio tuned to a blank channel (white noise), and the spirits use the static to form communications. Digital recorders are thought to have enough internal noise for the spirits to do their thing without outside white noise. In both cases, it is thought that the communication is generated electromagnetically within the circuit. This theory, of course, does not explain audible voices at the investigation site. Those phenomena are not EVP and must be explained in other ways."